564 



The fifth thoracic segment is entirely wanting, as well as its 

 appendages, and the appendages of the fourth thoracic segment, the 

 4. pereiopods , are represented , for one moult only, by rudimentary 

 exopodites, without endopodites. 



The outline of the life history of Leucifer is as follows. 

 -; The eggs are laid about nine o'clock in the evening, and they 

 develop very rapidly, hatching in about thirty six hours. They are 

 attached to the last pair of thoracic limbs, in a loose bunch of about 

 twenty eggs. 



Segmentation is regular and total. The fissures reach to the centre 

 of the egg^ and there is no central food-yolk, but a segmentation cavity 

 soon appears in the centre of the egg. During segmentation periods of 

 activity alternate with periods of rest. 



When the egg is divided into about seventy two spherules one side 

 becomes flattened, and the two spherules which occupy the centre of 

 the flattened area are pushed into the segmentation cavity, where they 

 probably give rise to the mesoderm. 



The primitive digestive cavity is formed, in the same place, by 

 the invagination of the flattened side of the egg, but the early stages 

 were not found in sufficient abundance to alloAv its later history to be 

 traced. 



In about thirty hours the appendages and eye spot of the Nauplius 

 can be seen inside the egg, and when the embryo is removed from the 

 egg it swims vigorously for a short time, but soon dies. 



It has a pear-shaped body, a very large labrum, a median ocellus, 

 a frontal sense organ, and three pairs of setose appendages. The first 

 antennae are uniramous, about as long as the body. 



The second antennae are of nearly the same length, and are bira- 

 mous, as are the much shorter mandibles. Four more pairs of appen- 

 dages are faintly indicated upon the ventral surface of the body, behind 

 the mandibles. 



The body and the appendages and setae are covered by a delicate 

 cuticle, which is soon cast off". 



Although these embryos soon died those which hatched naturally, 

 thirty six hours after the eggs were laid, could be reared without difficulty. 



The Nauplius, Yiooo inch long, presents some difi'erences from the 

 one just described. 



The body is ellipsoidal instead of pear-shaped. The uniramous 

 first antennae are faintly divided into five joints, and the terminal joint 

 carrys two long sensory hairs. 



The second antenna is the chief organ of locomotion. The endo- 

 podite is obscurely divided into three joints, and the exopodite is 



